Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit

TL;DR

This paper introduces synodyne detection, a method to detect complex squeezing spectra in quantum light, enabling force measurements beyond the standard quantum limit by accounting for measurement back-action.

Contribution

It proposes a novel detection scheme, synodyne detection, that reveals complex squeezing spectra and improves force measurement sensitivity in optomechanical systems.

Findings

Synodyne detection reveals complex squeezing spectra.

It enables force measurement sensitivity limited only by thermal occupation.

The method accounts for measurement back-action in continuous measurements.

Abstract

A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme, called synodyne detection, which reveals complex squeezing and allows the accounting of measurement back-action. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.